• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.482-484
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• 2005

The Modulation Transfer Function (MTF) is commonly used to characterize the spatial quality of imaging systems. This work is the attempt to measure the MTF at Nyquist frequency of the satellite imaging system what has 1m spatial resolution for KOMPSAT-2 image using the edge function. Artificial tarp targets are used in this study. A type of this tarp edge consists of two adjacent uniform bright and dark sides commonly used to test the performance of an optical system in edge function. The results from this work demonstrate the potential applicability of this method to estimate the response characteristics for KOMPSAT-2 that is scheduled to be launched.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.8
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• pp.340-348
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• 2003

In this paper, we propose a novel formulation to solve a time-domain combined field integral equation (CFIE) for analyzing the transient electromagnetic scattering response from closed conducting bodies. Instead of the conventional marching-on in time (MOT) technique, tile solution method in this paper is based on the moment method that involves separate spatial and temporal testing procedures. Triangular patch vector functions are used for spatial expansion and testing functions for three-dimensional arbitrarily shaped closed structures. The time-domain unknown coefficient is approximated as a basis function set that is derived from tile Laguerre functions with exponentially decaying functions. These basis functions are also used as the temporal testing. Numerical results computed by the proposed method arc stable without late-time oscillations and agree well with the frequency-domain CFIE solutions.

• Journal of Korean Association for Spatial Structures
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• v.22 no.3
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• pp.33-40
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• 2022

Recently, cultural heritages in South Korea gain many interests of restoration and preservation from the government since many of that have been severely damaged during earthquakes. Many previous studies in both terms of experimental and analytical approaches have been done to examine structural behavior and decide appropriate methods of preservation. Being motivated by such researches, this research aims to investigate a religious stone pagoda dated back to the Goryeo Dynasty in Korea. The structure consists of a granite stone foundation and baked bricks, which resembles the shape of traditional pagodas. In order to examine the structural behavior of the pagoda, an analytical model is implemented using ANSYS, a comprehensive engineering simulation platform. For the time history analysis of the pagoda, several earthquake excitations are chosen and input to simulation modeling. Seismic response of the tower such as time domain, natural frequency, modal shapes and peak acceleration measured at each layer are presented and discussed. In addition, the amplification ratio of the tower is calculated from the accelerations of each layer to determine tower stability in accordance with Korean seismic design guide. The determination and evaluation of status and response of the brick tower by simulation analysis play an important role in the preservation of history as well as valuable architectural heritages in South Korea.

• Journal of the Korean Society of Radiology
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• v.15 no.5
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• pp.705-713
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• 2021

The modulation transfer function (MTF) is calculated to analyze the resolution of the spatial frequency of the image acquired from the x-ray imaging system. In general, the response function of the detector acquires a line spread function (LSF) using a slit-camera, and derives a modulation transfer function through a Fourier transform. Because of the fact that the x-ray must always be incident on the center of the slit-camera, the tilt of the detector and slit-camera caused by the experimenter will affect the detector performance. In addition, if the tilt increases, the performance evaluation of the x-ray image system will be problematic. In this study, we analyzed the experimental and analytical models in the modulation transfer function, ie, the Fourier domain, based on the experimental error and analyzed the effect on the spatial frequency. Furthermore, performance evaluation is being carried out for various x-ray imaging systems, and experimental errors are indispensable, and the extent to which they can be tolerated should be reviewed.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1861-1863
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• 1996

In this paper, measurements and analyses of ELF electric fields in the vicinity of UHV overhead transmission lines and substations have been conducted. Planar-type sensors have been developed with special consideration of picking up lower frequency and spatial components without any distortion. So finally the electric field measuring system has the frequency bandwidth of 7[Hz] to 2.7[MHz] and the response sensitivity of 0.094[mV/V/m]. A brief description of design rules of the measuring system and measurement procedures is introduced. The actual survey near 154 and 345[kV] overhead transmission lines and power subststions was carried out and analyzed. It may be inferred from these results that the electric field intensity exeeds 7[kV/m] only in very few cases particularly at the substations so that the field measurements meet almost limits or guidelines that various authorized international institutes recommend.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1813-1815
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• 1996

With the three dimensional magnetic field measuring system dealt with in this paper, accurate measurements and analyses of ELF magnetic fields in the vicinity of UHV overhead transmission lines and substations have been conducted. For the field measurements multiturn loop-type sensors have been developed with special consideration of taking lower frequency and spatial components without any distortion. So the measuring system has the frequency bandwidth of 8[Hz] to about 53[kHz] and the response sensitivity of $9.88[mV/{\mu}T]$ in average. A brief description of design rules of the measuring system and measurement procedures is given. The actual surrey near 154 and 345[kV] overhead transmission lines and power subststions was carried out and analyzed. It may be inferred from these results that the maximum magnetic field intensities under typical UHV overhead transmission lines do not exceed $20[{\mu}T]$ so that the field measurements satisfy sufficiently all limits or guidelines that various authorized international institutes recommend.

• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1461-1469
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• 2004

Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by a linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analyses are conducted in the combustors without and with acoustic resonator, which is one of the acoustic-damping devices or combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in good agreement with the measurement data. In this regard. the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. From the numerical results for the combustor with present acoustic resonators installed, the acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity. It is found that the resonators with present specifications are not optimized and thus, the improved specification or design is required.

• 한국공간정보시스템학회:학술대회논문집
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• 2004.05a
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• pp.161-168
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• 2004

The dynamic instability of snapping phenomena has been studied by many researchers. Few papers deal with dynamic buckling under loads with periodic characteristics, and the behavior under periodic excitations is expected to be different from behavior under STEP excitations. We investigate the fundamental mechanisms of the dynamic instability when the sinusoidally shaped arch structures are subjected to sinusoidally distributed excitations with pin-ends. The mechanisms of dynamic indirect snapping of shallow arches are especially investigated under not only STEP function excitations but also under sinusoidal harmonic excitations, applied in the up-and-down direction. The dynamic nonlinear responses are obtained by the numerical integration of the geometrically nonlinear equation of motion, and examined by Fourier spectral analysis in order to get the frequency-dependent characteristics of the dynamic instability for various load levels.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1292-1297
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• 2004

Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by adopting linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analysis are conducted in the combustors without and with acoustic resonator, which is one of combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in a good agreement with the measurement data. In this regard, the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. The acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity.

• Journal of IKEEE
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• v.26 no.3
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• pp.475-482
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• 2022

Signal pre-processing and post-processing are some areas of study around electrical resistance tomography due to the low spatial resolution of pixel-based reconstructed images. In addition, methods that improve integrity and noise reduction are candidates for application in ERT. Lately, formulations of image processing methods provide new implementations and studies to improve the response against noise. For example, compact variational mode decomposition has recently shown good performance in image decomposition and segmentation. The results from this first approach of C-VMD to ERT show an improvement due to image segmentation, providing filtering of noise in the background and location of the target.